1. Field of the Invention
The present invention relates in general to antenna structures, and in particular to a dual band antenna structure in a wireless communication device.
2. Description of the Prior Art
The development of wireless local area network (WLAN) technology has been attended by the development of devices operating under the IEEE 802.11b standard (in the 2.45 GHz band) and the IEEE 802.11a standard (in the 5.25 GHz band). These devices benefit from dual band antennas.
U.S. Pat. No. 6,204,819 discloses a conventional dual-band antenna. The dual-band antenna includes a first and second conductive branches and is provided for use within wireless communications devices, such as radiotelephones. The first conductive branch has a first and second feeds extending therefrom that terminate respectively at a first and second micro-electromechanical systems (MEMS) switches S1, S2. The second conductive branch is in adjacent, spaced-apart relationship with the first conductive branch. One end of the second conductive branch terminates at a third MEMS switch S3 and the opposite end of the second conductive branch is connected to the first conductive branch via a fourth MEMS switch S4. The fourth MEMS switch S4 is configured to be selectively closed to electrically connect the first and second conductive branches such that the antenna radiates as a loop antenna in a first frequency band. The fourth switch S4 is also configured to open to electrically isolate the first and second conductive branches such that the antenna radiates as an inverted-F antenna in a second frequency band different from the first frequency band. However, the three dimensional structure of the antenna occupies a large space, which is counter to the trend toward miniaturization of portable electronic devices. Furthermore, the antenna adopts the switches to select two different frequency bands, which adds manufacturing cost and complexity of the antenna.
Hence, an improved antenna is desired to overcome the above-mentioned disadvantages of the prior art.